Effect of substitution of Mn3 by other trivalent cations on the colossal magnetoresistance and related properties of the manganates: La0.7A0.3Mn1−xMxO3 (A = Ca, Sr, Pb; M = Al, Cr, Fe, Co)

Investigations of the manganates of the general formula La0.7A0.3Mn1−xMxO3 with A = Ca, Sr, or Pb and M = Al, Cr, Fe, or Co in the x range 0.00–0.20 have shown that the ferromagnetic Tc and the insulator–metal transition temperature, TP, generally decrease with increase in x, accompanied by an increase in the resistivity at TP. The value of the saturation magnetization and, hence, the saturation moment also decrease with increase in x. The magnitude of magnetoresistance is generally smaller in the Fe and Co substituted systems when A = Pb. However, with A = Sr, we find enhanced colossal magnetoresistance in the 50–250 K range when x = 0.1 for M = Fe and Co. Interestingly, these systems exhibit a nearly flat resistivity curve over this temperature range.